Pump having multiple minimum flow mechanical stops

ABSTRACT

A pump is disclosed. The pump may have a housing, and at least one pumping mechanism disposed within the housing. The at least one pumping mechanism may have a variable displacement. The pump may also have a plurality of available mechanical stops. Each of the plurality of available mechanical stops may be connectable to the housing and configured the limit a minimum displacement of the at least one pumping mechanism to a different amount.

RELATED APPLICATIONS

The present disclosure claims the right to priority based on U.S. Provisional Patent Application No. 60/960,889 filed Oct. 18, 2007.

TECHNICAL FIELD

The present disclosure relates generally to a pump and, more particularly, to a pump having multiple minimum flow mechanical stops.

BACKGROUND

Hydraulic tool systems typically employ multiple actuators provided with high pressure fluid from a common pump. In order to efficiently accommodate the different flow and/or pressure requirements of the individual actuators, these systems generally include a pump having variable displacement. Based on individual and/or combined flow and pressure requirements, the pump changes a fluid displacement amount to meet demands. When demand is low, the displacement is reduced to conserve energy.

Typical variable displacement pumps used in hydraulic tool systems are known as swashplate or piston type pumps. This type of pump includes a plurality of pistons held against the driving surface of a tiltable swashplate. A joint such as a ball and socket joint is disposed between each piston and the swashplate to allow for relative movement between the swashplate and the pistons. Each piston is slidably disposed to reciprocate within an associated barrel as the pistons rotate relative to the tilted surface of the swashplate. As each piston is retracted from the associated barrel, low pressure fluid is drawn into that barrel. When the piston is forced back into the barrel by the driving surface of the swashplate, the piston pushes the fluid from the barrel at an elevated pressure.

The tilt angle of the swashplate is directly related to an amount of fluid pushed from each barrel during a single relative rotation between the pistons and the swashplate. And, based on a restriction of the pump and/or a fluid circuit connected to the pump, the amount of fluid pushed from the barrel during each rotation is directly related to the flow rate and pressure of fluid exiting the pump. Thus, a higher tilt angle equates to a greater flow rate and pressure, while a lower tilt angle results in a lower flow rate and pressure. Similarly, a higher tilt angle requires more power from a driving source to produce the higher flow rates and pressures than does a lower tilt angle. As such, when the demand for fluid is low, the swashplate angle is typically reduced to lower the power consumption of the pump.

Although efficient, lowering the swashplate angle too low may result in a sluggish hydraulic tool system. That is, when the angle of the swashplate must ramp up through a relatively large angle to produce a demanded flow rate and/or pressure, the time required for that movement may also be large. As such, the pump may be slow to produce a high flow rate and/or pressure when starting at a very low tilt angle. And, in some cases, movement of the hydraulic tool system may not be possible until the pressure of the fluid exiting the pump exceeds a predetermined threshold level. Thus, even after a demand for fluid is transmitted to the pump, the actuators may not immediately be capable of movement.

One way to improve pump responsiveness is to limit the minimum swashplate angle. For example, U.S. Pat. No. 5,567,123 (the '123 patent) issued to Childress et al. on Oct. 22, 1996 describes a swashplate type pump having a minimum allowable tilt angle. The swashplate angle is inhibited from being reduced below the minimum allowable tilt angle by way of a mechanical stop. That is, the mechanical stop engages the swashplate at the minimum angle to inhibit further reduction. In this manner, some flow from the pump may always be available for use by associated hydraulic actuators and, because the swashplate is always tilted to some degree, the time required to meet high fluid demands may be reduced.

While the pump of the '123 patent may effectively improve system responsiveness, the improvement may be insufficient or undesired in some situations. That is, based on the application at hand, the minimum swashplate angle may be too low or too high, resulting in low responsiveness or low efficiency. In addition, different machine operators may have preferences regarding the minimum pump flow that are not fully satisfied with a single fixed tilt angle limit.

The disclosed pump is directed to overcoming one or more of the problems set forth above.

SUMMARY OF THE INVENTION

In one aspect, the present disclosure is directed to a pump. The pump may include a housing, and at least one pumping mechanism disposed within the housing. The at least one pumping mechanism may have a variable displacement. The pump may also include a plurality of available mechanical stops. Each of the plurality of available mechanical stops may be connectable to the housing and configured to limit a minimum displacement of the at least one pumping mechanism to a different amount.

In another aspect, the present disclosure is directed to a method of pressurizing fluid. The method may include rotating a shaft to force fluid from a pumping chamber. The method may further include replacing a first component with a second component having a different effective length to change a minimum amount of fluid forced from the pumping chamber during a rotation of the shaft.

In yet another aspect, the present disclosure is directed to a pump kit. The pump kit may include a first mechanical stop connectable to a variable displacement swashplate type pump. The first mechanical stop may be configured to limit a minimum displacement tilt angle of the variable displacement swashplate type pump to a first angle greater than zero relative to a perpendicular of a driveshaft of the variable displacement swashplate type pump. The pump kit may also include at least a second mechanical stop connectable to the variable displacement swashplate type pump. The at least a second mechanical stop may be configured to limit a minimum displacement tilt angle of the variable displacement swashplate type pump to a second angle greater than zero relative to the perpendicular of the driveshaft of the variable displacement swashplate type pump. The pump kit may further include instructions for changing an effective displacement of the variable displacement swashplate type pump.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic illustration of an exemplary disclosed pump;

FIG. 2 is diagrammatic illustration of an exemplary pumping portion of the pump of FIG. 1;

FIG. 3 is a cross-sectional illustration of an exemplary mechanical stop for use with the pumping portion of FIG. 2; and

FIG. 4 is a cross-sectional illustration of another exemplary mechanical stop for use with the pumping portion of FIG. 2.

DETAILED DESCRIPTION

FIG. 1 illustrates a pump 10. In one embodiment, pump 10 may be driven by an external source of power (not shown), such as a combustion engine, via a driveshaft 12. As such, driveshaft 12 may extend from one end of a pump housing 14 for engagement with the engine.

As illustrated in FIG. 2, housing 14 may enclose a body 16 defining a plurality of barrels 18 (only one shown). Pump 10 may also include a plurality of plungers 20, one plunger 20 slidingly disposed within each barrel 18. Each barrel 18 and each associated plunger 20 may, together, at least partially define a pumping chamber 22. It is contemplated that any number of pumping chambers 22 may be included within body 16 and symmetrically and radially disposed about a central axis 24. In the embodiment of FIG. 2, central axis 24 may be coaxial with driveshaft 12. However, it is contemplated that central axis 24 may be at an angle relative to driveshaft 12 such as in a bent-axis type pump.

Body 16 may be connected to rotate with driveshaft 12. That is, as driveshaft 12 is rotated by the engine, body 16 and plungers 20 located within barrels 18 of body 16 may all rotate together about central axis 24.

Pump 10 may be a swashplate type pump. Specifically, pump 10 may include a stationary swashplate 26 having a driving surface 28 and a tilt frame 30. Driving surface 28 may be operatively engaged with plungers 20 by way of a joint 32 such as a ball and socket joint. That is, each plunger 20 may have a generally spherical end 34, which is biased into engagement with a cup-like socket 36. Sockets 36 may be configured to slide along driving surface 28, which may be fixedly connected to tilt frame 30.

Swashplate 26 may be tilted to vary a displacement of plungers 20 within barrels 18. Specifically, tilt frame 30 may be situated within a bearing member 38 and pivotal about a tilt axis 40. In one embodiment, tilt axis 40 may pass through and be substantially perpendicular to central axis 24. As tilt frame 30 and connected driving surface 28 pivot about tilt axis 40, the plungers 20 located on one half of driving surface 28 (relative to tilt axis 40) may retract into their associated barrels 18, while the plungers 20 located on an opposing half of driving surface 28 may be extended out of their associated barrels 18 by the same amount. As plungers 20 rotate about central axis 24, plungers 20 may annularly move from the retracted side of driving surface 28 to the extended side, and repeat this cycle as driveshaft 12 rotates.

As plungers 20 retract out of barrels 18, low pressure fluid may be drawn into barrels 18. Conversely, as plungers 20 extend into barrels 18, the fluid may be forced from barrels 18 at an elevated pressure. An amount of movement between the retracted position and the extended position may relate to a flow rate of fluid displaced by plungers 20 during a single rotation of driveshaft 12. Because of the connection between plungers 20 and driving surface 28, the tilt angle (angle relative to a perpendicular of central axis 24 that results in positive displacement of plungers 20) of driving surface 28 may relate to the movement between the retracted position and the extended position. One or more pressure relief valves (not shown) located within pump 10 or within a hydraulic circuit (not shown) supplied with fluid from pump 10, may affect the pressure of the fluid forced from barrels 18.

Swashplate 26 may be tilted about tilt axis 40 by way of an actuator 42. Actuator 42 may be disposed within a bore (not shown) of housing 14 and connected to tilt frame 30 by way of an arm 44 protruding from one side of tilt frame 30. Specifically, an actuator bracket 46 may be pivotally connected to protruding arm 44, and fixedly connected to actuator 42. Actuator 42 may translate linearly in the general direction of central axis 24 to pivot tilt frame 30 about tilt axis 40. For example, actuator 42 may move in a first direction away from an input end of driveshaft 12 to increase a tilt angle of driving surface 28. Conversely, actuator 42 may move in a second direction toward the input end of driveshaft 12 to decrease a tilt angle of driving surface 28. Actuator 42 may be powered in any conventional manner, including, among other ways, hydraulically, electrically, pneumatically, and mechanically.

In some situations, it may be desirable to limit a minimum tilt angle of swashplate 26. For this purpose, pump 10 may include a mechanical stop 48 disposed generally coaxially with actuator 42 in the bore of housing 14, and connected to housing 14 by way of one or more fasteners 50. In this location, mechanical stop 48 may inhibit the motion of actuator 42 in the second direction such that the resulting tilt angle of driving surface 28 ensures plungers 20 always extend into barrels 18 to displace fluid during the rotation of driveshaft 12 (i.e., mechanical stop 48 may always ensure positive displacement of pump 10). The minimum tilt angle of swashplate 26 may be directly related to the extension distance of mechanical stop 48 into the actuator bore of housing 14. That is, a longer mechanical stop 48 may limit the tilt angle of swashplate 26 to a greater angle, as compared to a shorter mechanical stop 48.

FIG. 3 illustrates one embodiment of mechanical stop 48. In this example, mechanical stop 48 resembles a plug having an extension length “L”. Extension length “L” may be considered the distance from an internal flange surface 51 to an end surface 52 that abuts actuator 42. In one embodiment, length “L” may be in the range of about 34-39 mm. A first embodiment of mechanical stop 48 may have a length “L” of about 34.6 mm. A second embodiment of mechanical stop 48 may have a length “L” of about 36.6 mm. A third embodiment of mechanical stop 48 may have a length “L” of about 38.6 mm.

The minimum tilt angle limit of swashplate 26 may be related to a responsiveness of pump 10. That is, a greater amount of time required for swashplate 26 to move from the minimum tilt angle to a desired tilt angle may result in a slow or sluggish pump. In contrast, a lower amount of time required for swashplate 26 to move from the minimum tilt angle to a desired tilt angle may result in a responsive pump. As movement of actuator 42 may be substantially constant, the time required for the movement of swashplate 26 may be directly related to the angular distance between the minimum tilt angle and the desired tilt angle. Thus, for a given desired tilt angle, a lower minimum tilt angle may require more movement time and, thus, result in a less responsive pump, as compared to a greater minimum tilt angle.

The minimum tilt angle limit of swashplate 26 may also relate to an efficiency of pump 10. That is, a greater minimum tilt angle of driving surface 28 may displace plungers 20 further into barrels 18 to pressurize a greater amount of fluid per revolution of driveshaft 12 during a standby condition, as compared to a lower minimum tilt angle. Thus, at the greater minimum tilt angle, the power source driving pump 10 may be loaded to a greater degree to pressurize a greater amount of unused fluid (the pressurized fluid may be substantially unused and drained to a low pressure tank during standby conditions). For this reason, a greater minimum tilt angle may result in a lower efficiency of pump 10 and the power source driving pump 10.

In some applications one of responsiveness and efficiency may be more important than the other. That is, in a first situation, responsiveness at the cost of efficiency may be desirable, while in a second situation, efficiency may be much more important than responsiveness. In the first situation, the mechanical stop 48 having the length “L” of 34.6 mm may be optimal. However, in the second situation, the mechanical stop 48 having the length “L” of 38.6 mm may be optimal. Thus, the length “L” may be selected for use based on an intended application of pump 10 and/or a machine incorporating pump 10. Alternatively, the length “L” may be chosen based on an operator preference.

To accommodate the different applications and/or operator preferences described above, a pump adjustment kit may be created having multiple mechanical stops 48. This kit may include one mechanical stop 48 of each length “L”. In addition, the kit may include instructions for removing the existing mechanical stop 48 and inserting a replacement mechanical stop 48 having a different length. The kit may have a single part number, meaning that the kit can be ordered and distributed as a single sales item to consumers. In some embodiments, replacement fasteners and a sealing member such as a gasket or o-ring 56 may be included in the kit for attaching the replacement mechanical stop 48 to housing 14.

In an alternative embodiment illustrated in FIG. 4, the kit may not include any or only a single length mechanical stop 48. In order to vary the minimum tilt angle of swashplate 26, one or more spacers 54 may be included in the kit for placement between internal flange surface 51 of the existing or the only replacement mechanical stop 48 and an external surface of housing 14. In one embodiment, multiple spacers 54 having different thicknesses may be included in the kit. For example, a first spacer 54 a may be included in the kit that has a first thickness “T”, while a second spacer 54 b may be included in the kit that has a second thickness “t”. In one embodiment, a difference in thickness between “T” and “t” may be about 2 mm. In this manner, a service technician may select a specific combination of spacers 54 a and 54 b to fine tune a distance that mechanical stop 48 extends into the actuator bore of housing 14 (i.e., to adjust the minimum tilt angle of swashplate 26).

INDUSTRIAL APPLICABILITY

The disclosed pump finds potential application in any fluid system where responsiveness and performance customization is desirable. The disclosed pump finds particular applicability in hydraulic tool systems, especially hydraulic tool system for use onboard mobile machines. One skilled in the art will recognize, however, that the disclosed pump could be utilized in relation to other fluid systems that may or may not be associated with hydraulically operated tools. For example, the disclosed pump could be utilized in relation to an engine lubrication, cooling, or fueling system.

Referring to FIG. 2, when driveshaft 12 is rotated, body 16 and plungers 20 disposed within barrels 18 of body 16 may also rotate. As plungers 20 rotate about central axis 24, spherical ends 34 thereof, riding along angled driving surface 28 may cause plungers 20 to cyclically rise and fall in the axial direction of driveshaft 12 (i.e., to extend into and retract from barrels 18). This reciprocating motion may function to draw fluid into pumping chamber 22 and push the fluid from pumping chamber 22 at an elevated pressure.

During operation of pump 10, the flow rate and/or pressure of the fluid exiting body 16 may be varied to meet demands of the associated circuit (not shown). To increase the flow rate and/or pressure of the discharged fluid, the tilt angle of driving surface 28 may be increased, by moving actuator 42 in the first direction away from the input end of driveshaft 12. Conversely, to decrease the flow rate and/or pressure of the discharged fluid, the tilt angle may be reduced by moving actuator 42 in the second direction opposite the first. The tilt angle may be reduced until actuator 42 engages mechanical stop 48.

To vary the minimum tilt angle limit of pump 10, the effective extension length “L” of mechanical stop 48 into the bore of actuator 42 may be adjusted. Specifically, mechanical stop 48 may either be removed and replaced with a mechanical stop 48 having a different length, or removed and spacers 54 added to reduce the effective extension length.

Because of the adjustability of pump 10, the flow output thereof may be tailored to meet the specific application or operator preferences at hand. Specifically, the minimum flow output of pump 10 may be selectively increased to improve responsiveness or decreased to improve efficiency. And, these adjustments may be easily facilitated with use of the disclosed pump kit.

It will be apparent to those skilled in the art that various modifications and variations can be made to the pump of the present disclosure. Other embodiments of the pump will be apparent to those skilled in the art from consideration of the specification and practice of the pump disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope being indicated by the following claims and their equivalents. 

1. A pump, comprising: a housing; at least one pumping mechanism disposed within the housing and having a variable displacement; and a plurality of available mechanical stops, each of the plurality of available mechanical stops connectable to the housing and configured the limit a minimum displacement of the at least one pumping mechanism to a different amount.
 2. The pump of claim 1, further including a tiltable swashplate disposed within the housing and biased into engagement with the at least one pumping mechanism, wherein each of the plurality of available mechanical stops is configured to limit a minimum tilt angle of the swashplate.
 3. The pump of claim 2, wherein the at least one pumping mechanism includes a plurality of plungers reciprocatingly disposed within a plurality of barrels, wherein the plurality of available mechanical stops affects a relative movement between the plurality of plungers and the plurality of barrels.
 4. The pump of claim 3, wherein the plurality of plungers are radially arranged about a common axis and configured to rotate about the axis relative to the swashplate.
 5. The pump of claim 1, further including an actuator configured to tilt the swashplate to an angle corresponding to a demand for fluid.
 6. The pump of claim 5, wherein each of the plurality of available mechanical stops is configured to limit movement of the actuator.
 7. The pump of claim 5, wherein the actuator is hydraulically actuated.
 8. The pump of claim 1, wherein each of the plurality of available mechanical stops corresponds with a different application of the pump.
 9. The pump of claim 1, wherein each of the plurality of available mechanical stops corresponds with an operator preference relating to responsiveness and efficiency.
 10. The pump of claim 1, wherein each of the plurality of available mechanical stops ensure that some fluid is always being displaced by the at least one pumping mechanism.
 11. The pump of claim 1, wherein the plurality of available mechanical stops includes: a plug; and at least one spacer configured to limit an extension of the plug into the housing.
 12. The pump of claim 11, wherein the at least one spacer includes a plurality of spacers, and the minimum displacement of the at least one pumping mechanism is limited based on the number of the plurality of spacers connected between the plug and the housing.
 13. The pump of claim 12, wherein the plurality of spacers have different thicknesses, and the minimum displacement of the at least one pumping mechanism is limited based further in on the thickness of the plurality of spacers connected between the plug and the housing.
 14. The pump of claim 13, wherein the plurality of spacers includes at least two spacers having a different in thickness of about 2-4 mm.
 15. The pump of claim 1, wherein the plurality of mechanical stops includes at least two mechanical stops having a difference in length of about 2-4 mm.
 16. A method of pressurizing fluid, comprising: rotating a shaft to force fluid from a pumping chamber; and replacing a first component with a second component having a different effective length to change a minimum amount of fluid forced from the pumping chamber during a rotation of the shaft.
 17. The method of claim 16, wherein replacing the first component includes adding a spacer between the first component and a pump housing.
 18. The method of claim 16, wherein replacing a first component with a second component having a different effective length changes a tilt angle of a driving surface.
 19. The method of claim 18, wherein replacing a first component with a second component having a different effective length limits motion of an actuator connected to the driving surface.
 20. A pump kit, comprising: a first mechanical stop connectable to a variable displacement swashplate type pump, and being configured to limit a minimum tilt angle of the variable displacement swashplate type pump to a first angle greater than zero relative to a perpendicular of a driveshaft of the variable displacement swashplate type pump; at least a second mechanical stop connectable to the variable displacement swashplate type pump and being configured to limit a minimum tilt angle of the variable displacement swashplate type pump to a second angle greater than zero relative to the perpendicular of the driveshaft of the variable displacement swashplate type pump; and instructions for changing an effective displacement of the variable displacement swashplate type pump. 